Air consists of:

1. only oxygen
2. only nitrogen
3. only carbon dioxide
4. all of these.

Which of the following gases supports burning?

1. oxygen
2. nitrogen
3. carbon dioxide
4. water vapour

Air is a mixture because:

1. the components of air retain their individual properties.
2. energy change takes place when the components of air are mixed together.
3. the composition of air remains the same everywhere.
4. the components of air cannot be separated by simple physical methods.

Oxygen in air is:

1. 4/5 parts
2. 1/5 parts
3. 1/3 parts
4. negligible